Strategies for Heat Detection and Timing of Artificial Insemination

The bottom line when measuring reproductive performance of a dairy herd is days open/calving interval. Three major components of days open are:

Days to first service is determined by the voluntary waiting period (time after calving that allows for uterine involution and resumption of normal cycling activity) and heat detection efficiency. For many years, the popular recommendation was a 60 day voluntary waiting period. Following this guideline, the average days to first service would be approximately 70 days provided 100% of the heats were detected.

Presently, the regional average for herds participating in the DHI program with DRPC at Raleigh, North Carolina, (8991 herds) is 58 days for the voluntary waiting period and 95 days to first service. Additionally, approximately 40% of all cows are not bred for the first time by 100 days in milk. This means a 100% first service conception rate would be required to obtain a 12.5 month calving interval. For the majority of dairy herds, the average days to first service needs to be lowered if efficient reproductive performance is to be achieved. 

A voluntary waiting period is needed to allow involution of the cervix and uterus. The reproductive tract is typically back to normal size by 35 days after calving and the lining of the uterus is back to normal by 45 days after calving in uncomplicated pregnancies and births. The uterine horn that contained the calf will not reach the pre-pregnant size, but will be slightly larger. Any periparturient disease, such as retained placenta or uterine infection, will prolong the time needed for involution.

Resumption of cycling or the first ovulation usually occurs in normal cows about 21 to 25 days after calving. Most often, the first ovulation is "silent," meaning there are no signs of heat. Usually, the first cycle is shorter than normal, 16 to 17 days, after which the normal 21 day cycle resumes. Timing of first ovulation and return of normal cycles can be delayed by abnormal involution, most peripartum disorders (retained placenta and uterine infections), and negative energy balance.

There are consequences to lowering the voluntary waiting period to 45 days. In many herds, this has been done and, theoretically, reducing the voluntary waiting period from 60 to 45 days should lower days to first service by approximately 12 to 15 days. However, conception rates may be lower and days to pregnancy are usually reduced by less than seven days. Additionally, if a cow becomes pregnant at 45 days she will have a very short calving interval of 101/2 months and approximately 265 days in milk.

Cows with below average milk production should have a voluntary waiting period of 45 days. This is because the only way a below average producing cow can productively contribute to the dairy operation is to have a low calving interval. A 45 day voluntary waiting period for these cows will avoid an excessive number of days in late lactation, which is the period of lowest milk yield. 

All cows should have at least one service prior to 100 days in milk. The primary reason for extended days to first service is poor heat detection efficiency. However, inadequate body condition, prolonged negative energy balance, or a high incidence of periparturient disease will also increase days to first service by prolonging the period of postpartum anestrous. The goal should be to average 75 to 80 days to first service with 10% or less of the cows not receiving their first service by 100 days in milk.

Conception rate at first service should be at least 45%. A first service conception rate less than 40% may indicate cows are not physiologically ready to breed back. Possible causes for lowered conception rates should be explored. If conception rates increase with increasing service number, example first service 28%, second service 35%, and third service 50%, cows are not ready to conceive and possible causes should be examined. 

Target Breeding is an aggressive, proactive systematic breeding program utilizing a prostaglandin (Lutalyse®* or Estrumate®**). At this point, Lutalyse is more widely accepted. Cows are given a "setup" prostaglandin injection prior to the end of the voluntary waiting period and a prostaglandin injection is given every 14 days thereafter until detection of heat and artificial insemination (see Figure 1). The treatment is designed to push cows into the stage of the estrous cycle which contains a mid-cycle corpus luteum. During this stage, it is most responsive to the second administration of prostaglandin 14 days later. Generally with this program, cows are not inseminated if they exhibit heat following the initial prostaglandin injection. However, this is optional and cows observed in heat following the initial injection can be bred and thus, removed from the program.

 

Once a voluntary waiting period has been established for a herd, cows are listed chronologically according to calving dates. Cows within 14 days of the voluntary waiting period are administered the "setup" prostaglandin injection. For convenience, injections are usually given once a week to all cows that surpassed the specified target date. Fourteen days later, cows receive the first breeding injection of prostaglandin and are observed for heat and inseminated accordingly. Cows that are not observed in heat are re-injected 14 days later, observed for heat, and inseminated. Prostaglandin administrations are continued at 14 day intervals until heat is detected.

Some producers and veterinarians may prefer to examine cows that fail to exhibit heat after the third prostaglandin injection. Others may appointment breed at a specified time (usually 72 to 80 hours) after the third or fourth prostaglandin injection. 

While this program is available, it is new with limited information and limited research and field observations. Pregnancy rates have not been firmly established, but have been shown to be comparable to Target Breeding (see Table 1). Researchers have shown that administration with gonadotrophin releasing hormone (GnRH) six to seven days prior to prostaglandin injection increases the percentage of cows synchronized and reduces the time and variability to estrus. Conception rates are better for timed AI or appointed breeding with this program compared to appointment breeding following prostaglandin administration. An injection of GnRH followed by a prostaglandin seven days later, and then followed 36 to 48 hours later with a second injection of GnRH, has been shown to synchronize ovulation, not estrus (see Figure 2).

 

 

The first injection of GnRH is given at a random stage of the estrous cycle and causes either luteinization or ovulation of the largest follicle in approximately 85% of all cows injected. The prostaglandin injection regresses the corpus luteum or luteinized follicle induced by GnRH. A new dominant follicle forms and is available to be ovulated by the second GnRH injection given 36 to 48 hours after the prostaglandin injection. According to preliminary results from a relatively small number of breedings, the Ovsynch program compared to traditional methods of heat detection may be effective in improving the percentage of cows pregnant by 60 to 100 days in milk and may reduce the days to first breeding.

When a cow is observed in standing heat at an odd time according to the injection sequence, the cow should always be bred and the remaining injections discontinued. A small percentage of cows may show heat before the prostaglandin injection because the first GnRH injection failed to ovulate the dominant follicle or the follicle is not sufficiently mature to ovulate. Cows showing heat just before or just after prostaglandin injection tend to be mid-cycle (13 to 15 days), or they may be late-cycling cows that are coming into heat for the first time after calving.

Research indicates the Ovsynch program does NOT work very well with heifers. Generally, conception rates for heifers were not acceptable, about 40 percentage points (74% versus 35%) below breedings after detected heat following a Target Breeding program (see Table 1). 

Historically, the approach taken by management has been passive–wait for cows to cycle and detect heat for AI, rather than proactive which now can be accomplished by the incorporation of a systematic breeding program that induces heat or allows for appointment breeding without the need for heat detection. Systematic breeding programs could have a major impact on reproductive management of lactating dairy cows.

The need for visual observation for identification of cows in standing heat could be reduced with the Target Breeding program to a few days weekly and may even be eliminated with the Ovsynch Breeding program. This opens the door to various ways of managing AI and the calving interval. Managers could determine the beginning of the breeding period and could eliminate breedings that occur early (less than 60 days) and more commonly those extended beyond 100 days. Realistically, it would be very difficult to get all cows bred between 60 to 100 days in milk, even with the use of systematic breeding programs.

With Ovsynch, all cows are bred at a timed breeding 10 days after the initial prostaglandin injection. Consequently, all cows would be inseminated the first time at 75 to 80 days in milk depending on the status of the program. With the Target Breeding program, 80% to 85% of the cows should be inseminated after three injections which could be targeted at 60, 74, and 88 days in milk.

The voluntary waiting period and average days to first service are important components of an efficient reproductive management program. For efficient reproductive performance and maintenance of days in milk between 150 to 175 days, the average days to first service should be 75 to 80 days. The profile of days to first service is also important. Cows bred prior to the voluntary waiting period should only be those having below average milk production when compared to herdmates, and attempts should be made for every cow to be bred prior to 100 days in milk.

 

Research has shown that Target Breeding programs are cost effective (see Table 2) and may improve herd reproductive performance compared with more traditional programs that treat individual cows.

The cost effectiveness of the Ovsynch program needs to be evaluated using the information given in Table 2 as a guide along with farm-specific drug cost, heat detection rate, and conception rate. Systematic breeding programs, such as "Target Breeding" and "Ovsynch" should be explored as methods to maintain desired days to first service and efficient reproductive performance.